Solid-state imaging systems or imaging readers have been used, in both handheld and/or hands-free modes of operation, to electro-optically read targets, such as one- and two-dimensional bar code symbols, each bearing elements, e.g., bars and spaces, of different widths and reflectivities, to be decoded, as well as non-symbol or form targets, such as documents, labels, receipts, signatures, drivers' licenses, and payment/loyalty cards, each bearing alphanumeric characters, as well as pictures, to be imaged. A known exemplary imaging reader includes a housing either held by a user and/or supported on a support surface, a window supported by the housing and aimed at the target, and an imaging engine or module supported by the housing and having a solid-state imager (or image sensor) with a sensor array of photocells or light sensors (also known as pixels), and an imaging lens assembly for capturing return light scattered and/or reflected from the target being imaged along an imaging axis through the window over a field of view, and for projecting the return light onto the sensor array to initiate capture of an image of the target over a range of working distances in which the target can be read. Such an imager may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing and processing electrical signals corresponding to a one- or two-dimensional array of pixel data over the field of view. These electrical signals are decoded and/or processed by a programmed microprocessor or controller into information related to the target being read, e.g., decoded data indicative of a symbol, or into a picture of a non-symbol target.
In order to increase the amount of the return light captured by the sensor array, especially in dimly lit environments and/or at far range imaging and reading, the known imaging module may also have an illuminating light assembly for illuminating the target with illumination light from an illuminating light source, e.g., one or more light emitting diodes (LEDs) and illuminating lenses, for reflection and scattering therefrom. The known imaging module may also have an aiming light assembly for projecting an aiming light pattern or mark, such as a “crosshair” pattern, with aiming light from an aiming light source, e.g., an aiming laser or one or more LEDs, through aiming lenses on the target prior to imaging. The user aims the aiming pattern on the target to be imaged during an aiming mode prior to imaging and reading.
In the hands-free mode, the user may slide or swipe the target past the window in either horizontal and/or vertical and/or diagonal directions in a “swipe” mode. Alternatively, the user may present the target to an approximate central region of the window in a “presentation” mode. The choice depends on the type of target, operator preference, or on the layout of a workstation in which the reader is used. In the handheld mode, the user holds the reader in his or her hand at a certain distance from the target to be imaged and initially aims the reader at the target. The user may first lift the reader from a countertop or a support stand or cradle. Once reading is completed, the user may return the reader to the countertop or to the support stand to resume hands-free operation.
Although the known imaging readers are generally satisfactory for their intended purpose, one concern relates to the scanning resolution (also known as pixel resolution), often expressed by a value measured in pixels per inch (ppi). Scanning resolution refers to the size of the smallest target detail that the sensor array can resolve (assuming the focus of the imaging lens assembly is adequate), which is determined by the size of the detail in the target image projected onto the sensor array. Put another way, the scanning resolution can be defined as the size of the smallest detail on the target that a single pixel of the sensor array can resolve. The target image on the sensor array grows smaller as the distance to the target is increased. When the target image approaches (for instance) around the same size as a pixel, the end of the working range has been reached, simply because, if the target moves any further away than that, then the smallest detail can no longer be resolved by the sensor array.
It is standard for the controller of the known reader to energize an indicator, such as a beeper or an indicating light emitting diode (LED), to advise a user that a symbol target has been successfully decoded. Thus, if the user receives no such feedback when attempting to read a symbol target at one distance, then the user will simply move the symbol target and/or the reader to another distance until such feedback is received.
However, when reading a non-symbol or form target, such as a document, there is no such equivalent feedback. If the scanning resolution is low at a particular distance, then the captured image will lack sufficient detail, be blurry, and perhaps illegible, particularly if, for example, the captured image is subsequently used as an input to recognition software, such as facial or object recognition software, or optical character recognition (OCR) software, or optical mark recognition (OMR) software, or intelligent character recognition (ICR) software, etc. The user will not be alerted to the poor quality, or lack of sharpness, of the image being captured and is not guided to try and get a better quality, or sharper, image by perhaps changing the distance between the reader and the document.
Accordingly, there is a need to provide an arrangement for, and a method of, electro-optically reading a target, particularly a non-symbol target, by image capture, based on an evaluation of the scanning resolution based on the target distance and by providing user feedback, especially if a minimum scanning resolution setting is not met.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The arrangement and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.